The complete source for building, designing, and remodeling green homes
Do you really want to delete the list, ?
This won't delete the articles you've saved, just the list.
This feature has been temporarily disabled during the beta site preview.
Replies
Attached additional data
Bradley,
Dana will come along in a few hours, I'm sure, and tell you that your numbers are too high. A new building with 2,500 square feet above grade won't have a design heat loss of 83,000 Btu/h.
Your planned infiltration rate is confusing. If you meant that you expect "natural air changes per hour" -- or ACH (nat) -- to be 0.5, that implies a blower door test result of 10 ach50. That's really, really high.
You should plan for a better envelope: tighter (with less air leakage), with higher R-values, and perhaps with fewer (or better) windows. And I'm guessing that the fudge factor in your calculations is way too high.
General Opinions and Strategies:
1. Long before breaking ground, the heat loss calculations should be one of your most pressing "construction problems," particularly in Wisconsin.
2. I think I might rather live in your last house than a house with those figures.
3. If you are the "research-based" type of person, then the best person to get some figures back from(the initial figures, at least) is very possibly you.
4. Download and install the free (we paid for it with Federal taxes) BEopt software. You obviously already know something about the design parameters. With BEopt, in about 2 hours, you can get (hopefully) better figures than you have, AND easily try different wall constructions, insulation levels, infiltration rates, etc. to see the impact on energy usage.
5. Like Martin said, the figures you listed are probably high, although maybe not really high, considering you are looking for over 4,000 sq. ft. of conditioned space with high ceilings in Wisconsin.
OK, actually, the figures look like they might be for the Victorian.
6. With careful analysis, you don't need the 15% Equipment Oversizing Factor.
7. If you are not as much "research-based" as I think you might be, then you need some more informed help, possibly professional help, for these considerations.
Deleted
Bradley,
Q. "What is the best strategy for tightening up the envelope?"
A. This is a key area. If you are research-oriented, it's time to start researching. Here are some links to articles that will get you started:
Questions and Answers About Air Barriers
Blower Door Basics
Airtight Wall and Roof Sheathing
Pinpointing Leaks With a Fog Machine
Air Leakage Through Spray Polyurethane Foam
Getting the Biggest Bang for Your Air-Sealing Buck
One Air Barrier or Two?
Air Sealing With Sprayable Caulk
Air-Sealing Tapes and Gaskets
Air Sealing an Attic
Bradley,
It's a little difficult to answer your questions. A lot depends on just how much you can and want to research, and a lot depends on just how energy efficient you want things to be. "Reasonable" means sometimes widely different things to different people. For example, you say R50 attic. For me, I want and have more than that (R65-70) in climate Zone 4 (almost 5), and that has proven extremely reasonable to me. The beauty of BEopt is that you can try all sorts of combinations rather quickly and see how they pay off in energy savings AND costs, although I never used the cost features, because I wasn't overly concerned, and they can be speculative.
Some of your questions:
1. Not necessarily sloppy, but I think Rescheck is for codes, whereas BEopt is a pretty sophisticated
energy analysis software program, which also can provide financial analysis. BEopt is not the only answer, but it is based on a very sophisticated energy simulation engine (Energy Plus), and it's MUCH easier to use than using the Energy Plus software directly. I believe it is a really good answer, for research-based people, without the need to be a professional in the construction field.
2. Reasonable target? A lot of times "reasonable" is closely tied to money, even though it wasn't for me. BEopt can help with the money aspects. The point is, once set up, input variables can be changed quickly to see the affect on energy/money-related output.
6. "Standard fiberglass walls" usually implies unwanted thermal bridges. Energy-conscious architect should already know a lot about things we are saying here. GBA certainly has articles on external foam, also. You, in your position, may have to pick and chose just what subjects you want to research in more detail, but BEopt can show you the results of various wall designs, including custom configurations.